The present invention relates to the field of techniques for assembling motor-vehicle bodies or parts thereof. According to the prior art, assembly of motor-vehicle bodies or of sub-assemblies of said bodies is performed by means of spot welding of sheet-metal panels. Again according to the prior art, spot welding is performed by means of welding guns having respective welding electrodes that engage on opposite sides the sheet-metal panels that are to be welded. Welding is performed while the panels are clamped in the precise assembly position by means of clamping devices. Once again according to the prior art, the said clamping devices have a supporting structure, at least one first clamping element and one second clamping element that are carried by the supporting structure and can move with respect to one another between an open position and a closed position, in which they are designed to clamp together two or more sheet-metal panels, and a fluid cylinder mounted on the supporting structure for controlling the relative movement of the two clamping elements between their open position and their closed position.
In recent times, it has been, on the other hand, proposed to carry out assembly of the panels partially overlapping one another by means of the clinching technique, basically consisting in pressing the two panels, for instance, between a die and a clinching punch which permanently deform the panels in such a way as to obtain connection thereof. The advantage of clinching as compared to electric welding lies in a greater simplicity and smaller overall dimensions of the corresponding equipment, as well as in a longer working life of the clinching punches with respect to the welding electrodes, which, particularly in the case of galvanized sheet metal, involve waste of time on account of the need to replace them after a relatively limited number of cycles. As regards clinching punches, instead, these may have a working life in the region of 250 000 cycles, without requiring any maintenance operations.
The purpose of the present invention is to enable a rational and economically advantageous application of the clinching process to the assembly of panels, and in particular of sheet-metal panels forming part of a motor-vehicle structure.
With a view to achieving the above purpose, the subject of the present invention is a clamping device of the type specified above, comprising a supporting structure, at least one first clamping element and one second clamping element that are carried by the supporting structure and can move with respect to one another between an open position and a closed position, in which they are designed to clamp together two or more panels, and a fluid cylinder mounted on the supporting structure for controlling the relative movement of said first and second clamping elements, the said clamping device being moreover characterized in that it also comprises at least one first clinching element and at least one second clinching element, which are carried by the aforesaid supporting structure and can move with respect to one another between an open position and a closed position, in which they are designed to carry out clinching of the panels clamped between said first and second clamping elements, and control means for controlling movement of said first and second clinching elements.
Consequently, the device according to the invention constitutes an integrated clamping and clinching unit that is able to perform both the clinching operation and the operation of clamping of the sheet-metal panels that are to undergo clinching.
In a preferred embodiment, the aforesaid means for controlling movement of the first clinching element and second clinching element consist of the same fluid cylinder that controls the first and second clamping elements, and further comprise a mechanical transmission that operatively connects one of said clamping elements, which is mobile with respect to the other clamping element, to one of said clinching elements, which is mobile with respect to the other clinching element, in such a way that, following upon activation of said fluid cylinder, the two clamping elements reach their closed position before the aforesaid clinching elements reach their closed position.
The device according to the invention is therefore able to carry out the clamping operation and the clinching operation simultaneously in a rational and economically advantageous way, using the same control cylinder, preferably a pneumatic cylinder, for actuating both the clamping elements and the clinching elements.
The unit according to the invention affords the advantages of greater simplicity and smaller overall dimensions as compared to known devices which use, on the one hand, equipment that only performs clamping of the sheet metal and, on the other, electric-welding guns with the corresponding accessories (power-supply transformer, power-supply cables, etc.). Furthermore, as has already been said, the clinching elements have a considerably longer life than spot-welding electrodes.
The possibilities of application of the invention are general, both as regards bodies of motor vehicles or sub-assemblies thereof and as regards any other structure made of panels assembled together. Of course, the clinching operation affords, as compared to the spot-welding operation, also the advantage of enabling joining of panels made of metals that are not easy to weld together or of panels made of metal material and panels made of plastic material.
In a concrete embodiment, a plurality of devices of the type specified above are used for carrying out tacking of a motor-vehicle structure or of a sub-assembly thereof, namely for performing application of a minimal number of joining points that makes it possible to bestow a relatively stable geometry on the structure, after which the structure itself is finally assembled by spot welding which, however, can be performed without having to clamp the components of the structure in a precise assembly position, since the said position has been already ensured by the previous tacking step carried out by means of the devices according to the invention.